The long term goal of this research is to understand the mechanism of cell communication in controlling developmental pattern formation. Vulval development in the nematode Caenorhabditis elegans is a simple example of inductive pattern formation: three of six equipotent precursor cells are induced to generate vulval cells by a signal from the gonad. A number of genes including the let-60 ras proto-oncogene play key roles in a genetic pathway that specifies the vulval cell fates in response to the inductive signal. The proposed research uses both molecular and classical genetics to dissect the vulval signal transduction pathway. In addition to our continued characterization of the let-60 ras gene, we will identify and characterize genes acting downstream of ras including its effector. The research plan consists of three major parts. (1) Analysis of let-60 ras. The expression pattern of let-60 ras gene during development will be examined by whole mount staining of let-60 ras and its fusion gene products. The relationship between let-60 ras structure and function will be studied by analyzing mutations that alter its specific activities or interactions with other factors. (2) Analysis of the lin-45 gene which likely acts downstream of let-60 ras in the signal transduction pathway. The function and structure of the lin-45 gene will be determined by analysis of mutants and molecular cloning. The site of action of lin-45 during vulval development will be examined by mosaic analysis. The expression pattern of lin-45 and the relationship between its structure and function will also be studied. (3) Identification and characterization of new genes acting downstream of let-60 ras in the signal transduction pathway. Novel genetic screens will be carried out to isolate mutations that suppress the loss-of-function or gain-of-function, mutant phenotype caused by let-60 ras mutations. Genetic and molecular analysis of genes defined by these suppressors will lead to determination of their structures and functions. By using vulval development as a model system and the power of C. elegans genetics, the in vivo function of ras oncogene product and its interacting factors in signal transduction can be elucidated. Study of the molecular basis of cell interaction in specifying developmental pattern is thus closely related to the study of the of cancer. The analysis of suppressors of activated let-60 ras might also allow us to discover new ways to suppress ras-mediated cancer.